This invention relates to film transport apparatus and, more particularly, to such apparatus which finds ready application in a cine-video system and which is software controlled for ease of use.
Film transports having general application are well known to those of ordinary skill in the art, particularly in the field of cinematography or the like. The basics of a typical film transport include a film gate, through which film is transported, which defines a location at which photographic images on the film are projected, supply and take-up reels from which the film is unwound and to which the transported film is wound, respectively, and a means for driving the film which, typically, comprises a sprocket wheel having teeth to engage the usual apertures, or perforations, in the film to transport it through the film gate. This typical film transport is used in cine-video converters, whereby the photographic images on the film are converted to video signals for display on a typical video monitor. One application of cine-video converters is in the medical field and, particularly, in angiography such as in cardiac catherization laboratories for producing high resolution displays on a standard video monitor from 35 mm angiographic film.
While various video-related subsystems have been developed for the aforementioned cine-video converters, one major drawback in the acceptance of such converters resides in the film transport apparatus used therewith. The usual requirement of precise positioning of the photographic film at the imaging location, or film gate, has resulted in a complicated transport path between the supply and take-up reels, requiring careful threading of the film, which frequently becomes frustrating for one without sufficient experience and laborious even for a highly trained technician. Typical film transport apparatus have been known to damage or even destroy the film being transported.
Another difficulty associated with film transport apparatus used in prior cine-video systems relates to limited transport speed control. In many film transports, only a few predetermined transport speeds may be selected, such as a transport speed of 15 or 30 film frames per second. However, a user often wishes to transport the film at a variable speed, either to reach a desired frame rapidly or to observe movement of the photographed features displayed on the video monitor. But, since most film transports exhibit simple mechanical controls, selection from a desirably large range of speed variance often is not possible. Further, even in those film transports having a variable film transport speed selected by, for example, a rotary knob, angular movement of the knob results in a corresponding transport speed which, normally, exhibits a fixed proportionality between transport speed and knob rotation, thus requiring an undesirably large knob rotation to effect high speeds. Alternatively, if the rotary knob exhibits a wide dynamic range so that, for example, high speeds are attained by limited angular movement, it is difficult for all but specially skilled technicians to provide fine speed control at slow transport speeds with this control knob.
A still further drawback found in conventional film transport apparatus relates to the manner in which the supply and take-up reels are installed on the apparatus. Typically, film may be wound in what is commonly referred to as A or B configurations, wherein a supply reel unwinds in the counterclockwise direction when film has been wound thereon in A configuration; and the take-up reel rotates in the counterclockwise direction while film is being wound thereon. Film wound on the supply reel in B configuration results in clockwise rotation when such film is unwound while film being wound on the take-up reel in B configuration results in clockwise rotation thereof. Heretofore, for proper operation of the film transport apparatus such that film unwinds from the supply reel and winds onto the take-up reel easily and without spillage, it has been necessary for the user to know beforehand whether film is wound in the A or B configuration and install the reels properly. Often, a determination of the film winding configuration results in wasteful time and may prove to be frustrating.
Yet another disadvantage associated with conventional film transport apparatus used in cine-video systems is the general inability of such apparatus to stop before the supply or take-up reel reaches its end. For example, during forward movement of the film, if the user does not monitor the size of the supply reel closely, film may "fly off" that reel, thus requiring careful and often frustrating re-threading thereof. Likewise, as film is rewound from the take-up reel onto the supply reel, if the size of the take-up reel is not monitored closely, film may "fly off" and thus require re-threading before images on that film subsequently may be viewed.
Since a preferred application of a cine-video system is in the medical field, it is expected that highly qualified physicians will operate such systems; but they properly are more concerned with the information being displayed rather than the technical features and drawbacks of the system itself. Such physicians often lack the skill of a trained mechanical technician and should not have to be overly concerned with the difficulties of threading and operating the film transport apparatus.